Computer type brake analyzer

ABSTRACT

An apparatus for analyzing the performance of wheeled, land vehicle brake systems is described wherein means are provided for driving the vehicle wheels at a predetermined speed and the operator or computer controlled brake actuator selectively applies the brakes in a series of simple successive steps comprising the test sequence. The pedal force, or other actuating force, the brake effort exerted by each wheel, and the imbalance between the braking effort of opposite wheels is measured and recorded on a strip chart or fed to a computer, to determine if the measured values fall outside of a predetermined range of values representing acceptable deviations from standard values. Any deviation of the brake effort from the acceptable values, or excessive imbalance between opposite wheels at any point in the test sequence, may be used as a basis for diagnosing and identifying a specific brake malfunction. The system can be enlarged to simultaneously test the brakes on all wheels of a land vehicle.

BACKGROUND OF THE INVENTION

1. Reference to Copending Application

This is a divisional application of copending application Serial No.382,538, filed July 25, 1973, now U.S. Pat. No. 3,899,916 which is acontinuation in part of application Ser. No. 811,168 filed Mar. 27,1969, now abandoned.

2. Field of the Invention

The present invention relates to improved apparatus and systems fortesting and diagnosing faults in wheeled, land vehicle brake systems.The invention particularly relates to a computer controlled or automaticbrake analyzer system to provide a rapid and reliable analysis ofvehicle brakes for purposes of safety and to facilitate repair ofdefective components.

The present invention is of great importance and practical value becausefaulty or inadequate vehicle brakes are one of the significantcontributing causes to the ever increasing number of automobileaccidents. It is well known that brake malfunctions caused by neglect,rather than poor brake design, are responsible for essentially allinstances of faulty or inadequate vehicle brakes. Furthermore, in amajority of instances, the neglect of vehicle brakes is not intentional.Rather, the owner simply is not aware of the existence of potentiallyhazardous conditions.

It is frightening to discover that faulty vehicle brakes frequentlyrespond normally under average driving conditions. Consequently, thedriver is lulled into a sense of false security concerning the adequacyof his brakes, and, therefore does not have them inspected, and iscompletely surprised when a malfunction occurs during emergencydeceleration or sudden stops. It is perhaps more unfortunate that asignificant number of potentially hazardous, but easily repairable,brake malfunctions are not discovered during routine inspection solelybecause prior existing inspection methods and equipment do not exposethe.

SUMMARY OF THE INVENTION

The present invention relates to a brake testing apparatus of highintegrity, which will detect nearly all types of brake malfunction,identify which brake is subject to the malfunction, and further indicatewhether the factor causing the malfunction is mechanical, hydraulic orfrictional. In many cases an even more specific cause of the detectedmalfunction can be readily determined and an accurate repair ticketimmediately prepared. Furthermore, the present invention relieves thetest operator of the task of reading output instruments or manuallyrecording indicated values during the test procedure and thereby reducestest time while greatly increasing accuracy and reliability.

The brake analyzing apparatus of the present invention includes meansfor selectively driving the wheels of the test vehicle. Thus, each wheelof the vehicle is cradled between a separate pair of rolls rotatablysupported by bearings mounted on a frame assembly. A cradle-mountedelectric motor is provided as a prime mover for each set of rolls andarranged to drive only the rear rolls of the set through a flexiblecoupling. Other forms of prime mover can be used, such as a hydraulic orpneumatic motor, or an internal combustion engine. All of these areparticularly suitable for portable brake testing apparatus. The rollsare driven at equal controlled speeds up to 45 MPH or more and in thepreferred form of apparatus, the brake effort is proportional to thereaction force upon each motor housing and is individually measured foreach wheel by a pneumatic weighing unit, or force transducer.

In performing a test, the operator or a computer controlled brakeactuator applies predetermined forces to the brake pedal, or other brakeactuating means, of the test vehicle in a predetermined testingsequence. When the vehicle brakes are actuated, the braking effortproduced at each wheel is proportional to the reaction force upon thecorresponding motor housing and is measured by the pneumatic weighingunit or other suitable transducer. Alternatively, the load current,torque or speed change of each driving motor can be measured as anindication of the braking effort being applied to its associated wheel.In the case of hydraulic or pneumatic motors, the pressure will increasewith load and provide an indication of torque output.

The measured values of brake effort are monitored during the test periodand an output signal, i.e., in the form of an indicating lamp, isproduced when the values of brake effort fall within or outside of apredetermined range of acceptable values. The strongest or weakest brakeis also identified to facilitate repair work. Standard values of brakeeffort for different weight classes of vehicles may be stored in asuitable memory and the set of values associated with a vehicle of agiven weight class may be chosen by the operator in order to allowinterchangeable testing of vehicles of different weights. The outputsignals may take the form of a lighted display, punched cards or tape,or a printed sheet itemizing the necessary brake repairs.

An evaluation of the test results obtained is made against a set ofrealistic standard values previously determined through a carefulprogram of testing the behavior of vehicles equipped with brakes havingmalfunctions, repairing the malfunctions and again testing the behaviorof the vehicles with corrected brake systems. The standard valuesselected enable the behavior of the brakes of each vehicle tested to beclassified as satisfactory, marginal, or unsafe. Evaluation of the testresults is relatively simple and will identify nearly all conceivablebrake malfunctions. In most cases, an exact cause of the malfunction canbe identified by a specific symptom of the brake analyzer operation, andin all cases the cause or causes of the malfunction can be categorizedas either mechanical, hydraulic, or frictional, or a combination of twoor more of these factors.

In accordance with the present invention, an apparatus is provided foranalyzing the braking performance of a wheeled vehicle. The vehicle haswheel brakes associated with at least two of the wheels and a brakeactuator for simultaneously applying the brakes of said wheels. Theapparatus includes test means such as a dynamometer for rotating thewheels of the vehicle for a test period during which the brakes areapplied. The apparatus includes means responsive to the brake effortsignals for producing a brake engagement lag imbalance signalrepresentative of the difference between the braking effort of the twowheels when the last to engage brake has engaged after operation of thebrake actuator. The apparatus may further include means for comparingthe brake engagement lag imbalance signal with satisfactory and marginallimits and for producing appropriate output signals when the imbalancesignal exceeds or remains below the satisfactory and marginal limits.The apparatus may also include means responsive to the brake effortsignals for producing a signal identifying which brake engages last.

BRIEF DESCRIPTION OF THE DRAWINGS

The construction and operation of the invention, as well as additionalobjects and advantages thereof, will become apparent when the followingdescription is read in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a diagrammatic view of a brake testing apparatus in accordancewith present invention;

FIG. 2 is a plan view of the brake pedal control unit 332 of FIG. 1illustrating the placement of the operator's feet thereon in dottedlines;

FIG. 3 is a block diagram of a computer, control and sensor units foruse with the apparatus of FIG. 1;

FIG. 4 is a block diagram of analog to digital converters for convertingthe analog brake effort and pedal force signals to digital format;

FIG. 5 is a block diagram of certain vehicle test limit storage elementsfor use in the circuit of FIG. 3;

FIG. 6 is a block diagram of a programmer for use in the computer ofFIG. 3;

FIG. 7 is a block diagram of certain computer components for providingrolling resistance test data;

FIG. 8 is a block diagram of certain computer components for calculatingand storing the pre-hydraulic brake effort level; and

FIG. 9 is a block diagram of certain computer components for providingbrake engagement lag test data.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A computer controlled or automatic brake analyzer system for testingvehicle brakes is described in FIGS. 1, 2 and 3. Referring now to FIG.1, a four-wheeled vehicle is illustrated with the front wheels 11 and 12cradled between the rollers 14 through 17 of a motoring dynamometer. Therolls 15 and 17 drive the wheels during the test, as will appear later.The rolls 14, 15, 16 and 17 are rotatably supported by bearings mountedin a conventional frame assembly, not shown. The rolls and frameassembly may be arranged in any convenient manner to permit the wheelsof the test vehicle to be easily stationed thereon. In an exemplaryinstallation the frame assembly may be mounted in a pit with the rollsat the floor level so that the test vehicle may be readily driven on andoff the rolls. The rolls 15 and 17 are oriented so that they arefarthest from the front end of the vehicle during a test.

Cradle-mounted electric motor 21 and 22 provided as driving means forthe left and right rolls 15 and 17, respectively. The shafts of themotors are directly coupled to the shafts of the respective drive rolls15 and 17 by suitable flexible couplings (not shown). The front rolls 14and 16 are permitted to idle.

A careful balance of motor power and roll spacing is necessary in thedescribed apparatus in order to permit accurate simulation of on-highwayspeeds and braking conditions. Thus, it has been found that the brakeheat produced in stopping a vehicle traveling 60 MPH is about nine timeshigher than that produced in stopping from 20 MPH. A high integritytesting system must have sufficient power to produce such heat at thebrake friction surfaces in the time consumed in a normal highway stop.Thus, neglecting vehicle wind resistance as a retarding force, a 0.5 Gdeceleration of a 4000 lb. vehicle from 60 MPH to 0 MPH results in anaverage brake heating rate of 113 btu/sec over a stopping time of 5.48sec. This power requirement can be met by application of 40 horsepowerat each wheel to be tested.

Although on-highway brake friction surface rubbing velocities decreaseas the vehicle decelerates, it has been found that test integrity isaffected only at extremely high speeds resulting in low brakeapplication forces for a given heating rate and at speeds below thecritical rubbing velocity of the friction surfaces. Thus, integrity maybe retained when tests are performed at one speed so long as the speedselected falls within the wide limits set forth above.

Selection of a particular speed is also dependent upon the tractiveeffort between the driving rolls 15 and 17 and the tire tread. When avehicle tire is cradled between two rolls as shown in FIG. 1, pressuresless than road contact pressures are present between the tires and eachroll. The pressure normal to the roll surface is dependent upon both theroll spacing and the particular roll from which the turning force isapplied to the tire. Thus, it should be apparent that as the brakes areapplied against rotating drive rolls 15 and 17, the vehicle will tend tomove backward. This will reduce the tire contact pressure against theforward idle rolls 14 and 16 and increase the tire contact pressureagainst the rear drive rolls 15 and 17. Accordingly, application ofpower to the tires through the rear drive rolls 15 and 17, as shown inthe preferred embodiment, has the advantage of increasing thetire-to-roll contact pressure as the brakes are increasingly applied.

The motors 21 and 22 are controlled from a motor control unit activatedby computer 299 through lines 21c, d and e to provide a high torque, lowtorque and to stop. A pair of pneumatic lifts 300a and 300b arepositioned between the rolls as illustrated to lift the wheels 11 and 12off the rollers 14 through 17 in their raised position and therebypermit the test vehicle to be readily driven on and off of the rollers.Once the appropriate wheels are positioned between the rollers 14through 17, the fluid power lifts are operated by means of appropriateelectronic control units such as 302a. The electronic control unitsoperate conventional pneumatic lift units (303 in FIG. 1) to lower orraise the lifts in response to appropriate control signals on lines 304and 305, respectively from the computer 299. The lift control units 302asend back a lift lowered signal via line 306 to the computer 299indicative of the fact that the lifts are in a lowered position so thata selected testing sequence can begin.

Each motor 21, 22 is cradled as in a dynamometer so that a forcereaction can be measured from its housing, which is equal to the inputforce to the rolls and tires. Consequently, as the brakes are applied,their torque resistance to wheel rotation is proportional to motorhousing reaction. Since the right and left rolls are not interconnected,the retarding force from each brake can be independently measured by anysuitable electrical transducers which provide an output signalproportional to the torque between the respective housing of motors 21and 22 and the fixed frame. For example, brake effort signal generatingtransducers 38a and 39a are connected to the motors 22 and 21 to provideoutput signals representative of the torque applied by the drive motorswhich, in turn, is representative of the retarding force between therespective wheels and the drive rollers 15 and 17. Only one brake efforttransducer 39a is shown in FIG. 1 for purposes of illustration. For amore detailed discussion of transducers suitable for measuring the brakeeffort exerted on a motoring dynamometer, see British Pat. No. 1,284,498which issued on Dec. 6, 1972.

A pair of tachometer generators 307a and 307b are coupled to the drivenrollers 16 and 14 for providing d.c. signals to the computer via lines308a and 308b having an amplitude proportional to the speed of therespective driven roller. Only generator 307a is illustrated in FIG. 1.

The test vehicle illustrated in FIG. 1 is provided with conventionalbrake drums and shoes with the brake shoes 320 being forced outwardlyagainst the drums 321 by a manually controlled force responsive brakeactuator including a pair of conventional pistons 322 carried within awheel cylinder 323. Brake fluid is forced through brake lines 324 tooperate the wheel cylinder pistons 322 and apply the brakes by means ofa conventional master brake cylinder 325 including a piston 326 operatedby brake lever 327 in response to a force applied to a brake pedal 328.The brake lever 327 is biased by a spring 330 in a position to maintainthe brake pedal in its uppermost position to relieve the pressure in thebrake lines and permit the brake shoes 320 to be withdrawn from thebrake drum by conventional springs, not shown.

A brake pedal actuator control unit 332 for applying a programmed forceto the brake pedal 328 is described more particularly in the copendingapplication Ser. No. 382,538 filed July 25, 1973, and assigned to theassignee of this application. The unit 332 includes a frame 333 whichcomprises a pair of L-shaped legs which rest on the floor 334 of thevehicle under test. A foot treadle 335 is pivotally mounted at the lowerend of the frame 333. A piston 336 is mounted within a fluid powercylinder and forces a brake pedal bracket 337 against the brake pedal328 in accordance with the pressure of the fluid on the piston 336. Apedal force sensor (transducer) 338 is disposed between the bracket 338and the brake pedal 328 to provide an analog signal on line 340 which isproportional to the force applied to the brake pedal. A pedal-to-floordistance sensing unit 342 provides an output signal on line 343 when thepedal position has become less than the minimum acceptablepedal-to-floor distance.

The foot treadle 335 is biased outwardly away from the frame 333 bysuitable springs (not shown) with a force in excess of the maximum pedalforce required during the testing sequence. A foot pressure sensor inthe form of a micro-switch 345 is actuated when the force exerted by theoperator's feet on the treadle 335 exceeds the maximum anticipated pedalforce, causing the treadle to move downwardly a predetermined distanceagainst the spring bias. The foot pressure sensor 345 when actuatedproduces a foot pressure sensor signal on line 346 indicating that theoperator is placing sufficient force against the treadle 335 to preventmovement of the brake pedal actuator control unit while the brake pedalis operated at maximum force by the piston 336. Fluid under pressure isapplied to the piston 336 for operating the brake pedal via fluid line350 and pedal actuator transducer 351. A pedal position transducer (notshown) is suitably secured to the fluid power cylinder for generating asignal on line 348 which is proportional to the position of the piston336, for providing information concerning the brake pedal travel duringthe testing sequence as will be discussed in more detail.

The brake pedal control unit 332 is manually placed within the testvehicle at the beginning of the testing sequence. The operator guidesthe brake pedal bracket 337 until it engages the brake pedal 328 asshown in FIG. 1. An additional microswitch may be positioned on thebracket 337 to be actuated when the bracket engages the brake pedalthereby providing a signal indicating that the control unit is in place.Rather than remove the brake actuator control unit 332 from the vehicleduring the time that the vehicle is moved to change the pair of wheelsthat are positioned on the dynamometer rollers 14 through 17, thecontrol unit 332 may be left in the vehicle and the brakes controlled bythe computer. To provide this type of control, a treadle sensor signalproportional to the force applied by the operator to the treadle may beproduced by a suitable transducer and fed back to the computer via line354. The computer responds to the treadle sensor signal on line 354 toactuate the pedal actuator transducer 351 and apply fluid pressure tothe piston 336 which is proportional to the pressure of the operator'sfeet on the treadle. Such a transducer is described more particularly incopending application Ser. No. 382,538. The operator is thus providedwith reliable control of the braking action of the vehicle while it isbeing driven to place the rear wheels 11a and 12a on the dynamometerrollers.

Referring now to FIG. 3, the computer or automatic control system 299 isactuated by a manual control unit 353 to selectively commence the testsequence for the front or the rear wheels and to stop, via signals onlines 355, 356 and 357, respectively. The computer 299 receives inputsignals from the lift controls 302a and b indicating that the lifts arein the lowered position and the test vehicle wheels are properlypositioned for the test sequence. The computer also receives inputsignals from the brake effort transducers 38a and 39a, tachometergenerators 307a and 307b, foot pressure sensor 345, pedal-to-floordistance sensor 342, and pedal force sensor 338. The computer 299controls the induction motors 21 and 22 to provide high or low torque (yor Δ connection) or to stop, via signals on 21c, d, and e, respectively.The pedal actuator transducer 351 is controlled via signals on line 352to apply sufficient force to the vehicle's brake pedal to provide apredetermined brake effort from the strongest brake or a predeterminedpedal force as will be discussed in more detail.

The computer may provide output signals on line 361 for recording by aconventional recorder 362, for example, of the strip chart type ormagnetic type. The recorder 362 may also be in the form of a printerwhich provides a printed sheet indicating the condition of the vehiclebrakes, with or without recommendations as to suggested corrective workneeded, if any. The computer may also apply output signals on line 363to a visual display arrangement 364 such as a group of lights to providea recorded indication of appropriate output signals indicating thatcertain braking characteristics are satisfactory, marginal orunacceptable. The visual display arrangement provides a recordation ofsuch output signals for a time duration in excess of the testing periodso that the operator may review the braking performance after thetesting sequence has been performed on front, rear or both sets ofwheels of the test vehicle.

To determine whether or not the braking performance of the vehicle undertest is satisfactory, marginal or unacceptable, pre-established testlimits are fed into the computer on line 365 from a vehicle test limitsstorage arrangement 366, shown in more detail in FIG. 6.

The computer 299 operates on digital signals and thus includesconventional analog-to-digital converters for converting analog inputsignals into corresponding digital signals. Analog-to-digital convertersfor providing digital right and left brake effort signals and pedalforce signals are illustrated in FIG. 4. Analog signals from the rightand left effort transducers 38a and 39a are amplified by amplifiers 370aand 370b & converted to binary signals by analog-to-digital converters371a and 371b. The binary signals representing the right and left brakeefforts are supplied on lines 372a and 372b to logic and storageelements within the computer as will be described in more detail. Thelines such as 372a and 372b for carrying digital information in the formof multi-bit words between the various computer components illustratedin the drawings are composite lines, that is, one line is used for eachbit or N lines for an Nth bit word to transfer the data in parallelform. Thus, each digital data transmission line as shown in the drawingsrepresents a composite of Nth lines.

A subtractor 374 subtracts the digital signals representing the rightand left brake efforts to produce a braking effort imbalance signal online 375. Analog signals representing the separate brake effort signalsare also supplied to certain computing components via lines 373a and373b. The right and left brake effort signals on lines 372a, 372b, 373aand 373b represent the gross braking effort or the total retarding forcebetween the left or right wheel 11 or 12 and the respective drive roller15 or 17. During the time that the brakes are not being applied to thevehicle, the signals on lines 372a, 372b, 373a, and 373b representrolling resistance of the respective wheels and when the brakes arebeing applied, these signals represent the sum of the rolling resistanceand the braking effort contributed by the brake drum and shoe of therespective wheel.

The brake effort imbalance signal on line 375 represents the grossimbalance in the retarding force between the wheels 11 and 12 and therespective drive rollers and thus includes the rolling resistanceimbalance of the two wheels. The subtractor 374 also applies an outputsignal on line 376 having a logic sign (high or low) dependent uponwhich brake effort signal is the largest. The logic sign of the signalon line 376 thus identifies the strongest (and weakest) brake. Forexample, a true logic signal (high level) on line 376 may be utilized toindicate that the highest brake effort is supplied by the right brakeand a false logic (low level) signal may be used to indicate that theleft brake is strongest.

A gate 379 receives the highest brake effort identification signal (trueor false) and switches the highest brake effort signal (right or left)to an output line 378. The analog signal from the pedal force sensor 338is also amplified by amplifier 380 and converted via ananalog-to-digital converter 381 to a binary signal representative of theforce applied to the brake pedal 328 (FIG. 1) by the pedal actuator 332(FIG. 1).

Referring now to FIG. 5, there are illustrated vehicle test limitsstorage elements 384a through 384jj for supplying digital signalsrepresenting satisfactory, marginal and unacceptable limits of brakeperformance of the vehicle under test and the brake effort levels atwhich the tests are to be conducted. The storage elements of FIG. 5provide a total of thirty-six output signals on lines 385a through 385jjto the computer. The circuit associated with each of the output lines385a through 385jj may be of the type shown in FIG. 6 of copendingapplication Ser. No. 382,538. The output signal for any line 385athrough 385jj may represent 2¹⁰ or a total of 1024 discrete values.

The storage element 384a of FIG. 5 determines the total brake effortrequired (front plus rear wheel brakes) for the high level brake efforttests for the particular vehicle. The high level brake effort signal online 385a may be selected from as many as 1024 discrete values but as apractical matter may be limited to 5 values representing categories ofweight of the vehicles being tested. Such categories may, for example,represent (1) small cars, (2) intermediate compacts, compact cars, (3)heavy compact cars, (4) standard cars, and (5) heavy cars. The storageelement 384b provides an output signal on line 385b which represents thebrake effectiveness percentage between the front and rear wheels of thevehicle under test. For example, the storage element 384b may be set toprovide a brake effectiveness of 75% for the front wheels and 25% forthe rear wheels, or 60% for the front wheels and 40% for the rearwheels, etc. A one percent variation may be utilized if desired. Thestorage element 384c provides an output signal representing thepre-hydraulic brake effort factor X₁ which is utilized by the computerto arrive at the degree of braking effort utilized to derive certaintest data from the vehicle in pre-hydraulic tests as is described inmore detail in copending application Ser. No. 382,538. The storageelement 384d provides an output signal which represents a comfort levelbrake effort factor X₂ which is utilized by the computer to derive thecomfort level brake effort at which brake effort imbalance of thevehicle is measured as is described in copending application Ser. No.382,538. The storage element 384h, i and j provides output signals onlines 385h, 385i and 385j which represent the satisfactory, marginal andinvalid limit of brake effort imbalance for the brake engagement lagtest. The remaining storage elements provide signals representingsatisfactory, marginal or acceptable limits for other brake tests forthe particular vehicle under test and the value of such signals may bevaried in accordance with braking performance requirements dictated bygovernmental agencies, etc.

It should be noted that only two output signals are utilized from eachof the storage elements 384stuv and 384wxyz at any one time, and the twoparticular output signal lines that are read by the computer will bedetermined by the type of brake incorporated into the test vehicles,that is, manual or power brakes.

The vehicle test limit information stored in elements 384a through 384iimay, of course, be supplied to the computer by other well knownrecording means such as punched cards, magnetic tape, etc.

A computer programmer is illustrated in FIG. 6 for providing thecommands for a complete testing sequence for the front and rear wheelsof the test vehicle. The manual control 353 initiates the testingsequence for the front wheels by an appropriate signal on line 394 andinitiates the testing sequence of the rear wheels by a signal on line395. The manual control unit stops the test program and the dynamometermotors by a signal on line 396. A signal on line 394 or 395 actuates apreprogram storage register 400 to provide a signal on line 304 to causethe lift control units to lower the lifts and cradle the front wheelsbetween the rollers 14 through 17. The storage register 400 alsoprovides a signal on line 352 to the pedal actuator transducer 351 tocause the brake pedal actuator 332 to lower the brake pedal bracket 337until contact is just made with the brake pedal 328. The brakes are notapplied by the signal on line 352 from the register 400.

As shown in FIG. 6, signals on lines 394 and 395 from the manual control353 are also applied to front and rear wheel test inhibitors 402a and402b. The wheel test inhibitors also receive signals from the footpressure sensor 345 via line 346 and from the lift control units vialine 306. An appropriate signal (true or false) on all input circuits ofeither wheel test inhibitor will provide an output signal (i.e. true) onthe respective output lines 403 and 404 or 407, 408 and 409.

Front and rear wheel lamp indicators 410 and 412 are responsive tosignals on lines 403 and 407 to indicate which set of wheel brakes areundergoing tests. An output signal on line 404 or 409 initiatesoperation of the motor control 413 which, in turn, applies anappropriate signal on output line 21d to energize the inductiondynamometer motors 21 and 22 in a low torque configuration, e.g. Yconnection. The dynamometer motors rotate drive rollers 15 and 17 which,in turn, rotate the left and right wheels of the vehicle. The vehiclewheels, in turn, drive the driven rollers 16 and 14 which rotatetachometer generators 307a and 307b. Under certain abnormal conditionssome slippage may occur between the tires and the drive rollers 15 and17 which causes the driven rollers 14, 16 to rotate at a slower speedthan the drive rollers 15, 17. The coefficient of friction, influenced,for example, by water between the tires and rollers is an importantfactor in determining slippage. Thus, the driven rollers 14 and 16 willbegin to catch up to the drive rollers 15 and 17 as the surface of thetires dry off.

Each of the tachometer generators 307a and 307b produce a d.c. signalhaving a magnitude proportional to the rotational speed of therespective driven rollers 16, 14. The signals from the tachometergenerators are supplied to one input of a pair of differentialamplifiers 416 and 418. The other input of each of the differentialamplifiers is connected to a reference voltage source 417. Thedifferential amplifiers 416 and 418 are arranged to provide anappropriate output signal (high level) to a gating circuit 414 only whenthe output signal from the respective tachometer generator exceeds thereference voltage. An output signal from each differential amplifier isindicative of the fact that both driven rollers are within apredetermined range of the normal induction motor speed representing,for example, a vehicle speed of 45 MPH.

A gating circuit 414 produces an output signal on line 420 in responseto output signals from both comparators 416 and 418 and an output signalon line 404 or 409. The output signal on line 420 causes the motorcontrol unit 413 to change the energization of the drive motors to ahigh torque configuration e.g., Δ connection, via a signal on line 21c.An output signal on line 420 is also supplied to a program commandstorage 422 to initiate time sequence test commands to the variouscomponents of the computer as will be described in more detail. Forexample, the program command storage provides command signals to a frontto rear pedal force balance command control unit 425. The unit 425 inresponse to the command signal from storage 422 and a signal from therear wheel test inhibitor via line 408 provides a signal to the pedalactuator transducer 351 to actuate the brakes in the front to rear pedalpressure balance tests to be described.

The program command storage also provides appropriate signals to commandunit 427 to initiate a static pedal force and pedal to floor test. Atthe end of a test sequence, the program command storage supplies asignal to an end of test control unit 430 which sends a signal on line305 to the lift control units to raise the lifts so that the vehicle maybe moved. A manual pedal control unit 432 when enabled by a signal fromunit 430 responds to a signal from the treadle pressure sensor on line354, and provides a signal proportional thereto on line 352 to controlthe brake pedal actuator 332 in accordance with the operator's footpressure on the treadle. This permits the vehicle to be moved withoutremoving the actuator 332. The manual pedal control unit 432 isinhibited by a signal on either line 404 or 409 indicating that a testsequence is still under way. Fast and slow rate pedal force controlunits 434 and 435 apply signals to the pedal actuator transducer 351 toprovide a fast or slow rate of brake application as will be described.

The detailed function of the components of the automatic control system299 for controlling the vehicle brakes and for monitoring the brakingeffort signals etc., in a multi-step testing sequence is described indetail in my copending application Ser. No. 382,538. Only thosecomponents and testing steps which relate to the present invention ofapparatus for evaluating brake engagement lag data are described indetail here.

Preparatory to commencing the test sequence, it is necessary that eachof the vehicle test limit storage elements 384a through 384jj beadjusted to provide the appropriate output signal. The category ofweight of the vehicle, i.e., compact, etc., percent of balance betweenfront and rear brakes, use of power or manual brakes are reflected byappropriate adjustments in storage elements 384a and 384b, 384stuv and384wxyz. The acceptable or marginal and fail limits as established bythe remaining storage elements will remain the same for many vehicles.

An anti-skid and limited slip differential switch may also be manuallyset by the operator prior to the commencement of the test sequence. Ananti-skid switch (not shown) permits the operator to determine whetherthe anti-skid test will be performed on the front and/or rear wheelbrakes. A limited slip differential switch (see FIG. 8) permits theoperator to override an abort command when the maximum rollingresistance of either wheel exceeds a preset maximum limit as isdescribed in more detail in connection with FIG. 7.

To initiate the test sequence, the vehicle is driven into the test areauntil the front wheels are positioned between the dynamometer rollers 14through 17 (FIG. 1). The brake pedal actuator control unit 332 ispositioned over the brake pedal and the pedal bracket 337 is guided intoengagement with the brake pedal. The manual control 353 is then actuatedby the operator while seated behind the vehicle steering wheel toinitiate testing of the front wheels.

Referring now to FIG. 6, the hydraulic lifts are lowered by thepreprogrammed storage register 400 and the motors are energized in thelow torque configuration as discussed previously. When the drivenrollers 14 and 16 have reached a predetermined percentage of the test orinduction motor speed, i.e. 75%, the gating circuit 414 actuates themotor control 413 to energize the dynamometer motors in the high torqueconfiguration. The gating circuit 414 also provides a signal to theprogram command storage which, after a predetermined time delay, forexample, two seconds to enable the dynamometer rollers to arrive at thefinal test sequence speed, e.g. 45 MPH, issues test commands to thevarious components to the system to begin the testing operation.

ROLLING RESISTANCE STORAGE AND EVALUATION TEST

The maximum rolling resistance and the rolling resistance imbalance aremeasured and compared with maximum, satisfactory and marginal presetlimits by the computer components illustrated in FIG. 7. The rollingresistance of each wheel is also stored during this testing step for usein later testing steps in providing the net brake effort imbalance. Theprogrammer illustrated in FIG. 7 is shown only in block form andreferenced by the number 440. The programmer initiates operation of thevarious components of FIG. 7, i.e., gates and storage elements andcontrols the brake pedal actuator via signals to the transducer 351 tomaintain the brakes in a released or inoperative condition. The signalson lines 372a and 372b thus represent the rolling resistance of theright and left wheels of the vehicle. The rolling resistance signals areapplied to a dual subtractor 442 and stored in storage elements 455 and456. The subtractor 442 subtracts the right and left rolling resistancesignals from a maximum limit rolling resistance signal from storageelement 384e. The subtractor 442 applies a first output signal (e.g.high level) on fail lines marked F, to associated gates 446 or 447 wheneither rolling resistance signal exceeds the maximum limit signal fromelement 384e. The gates 446 and 447 are enabled by an appropriatereadout command signal from the programmer 440 and in response to a failsignal from the dual subtractor 442 to energize a fail lamp indicator452 or 453, respectively, indicating that the rolling resistance of therespective wheel has exceeded the acceptable limit. The satisfactoryindicating lamps 450 and 451 are energized when the subtractors apply asecond output signal on S or satisfactory lines to the gates 446 and 447indicating that the rolling resistance is less than the maximumacceptable limit. The indicating lamps 450 through 453 remain energizedby an appropriate latching circuit to be discussed, until after the testsequence has been completed to provide a recorded indication that thevehicle has passed or failed the maximum rolling resistance test. Theindicating lamps referred to in the remaining figures also remainenergized for a period in excess of the test period to provide a recordof the test results.

The automatic control system of the present invention includes a limitedslip differential switch 448 and a limited slip differential abortcommand gate 449 as shown in FIG. 7. A fail signal on line F from thedual subtractor 442 is also applied to the programmer 440 via abortcommand gate 449 to stop the testing sequence and de-energize thedynamometer motors 21 and 22. The limited slip differential switch 448when operated to indicate that the vehicle being tested is equipped withlimited slip differential inhibits the abort command gate 449 during therear wheel testing sequence so that a fail signal on line F from thesubtractor 442 does not stop the testing sequence.

During the rolling resistance test, the highest rolling resistancesignal on line 378 is stored in storage element 457 for later use. Thebrake imbalance signal on line 375 is also stored in storage element 458and compared with the satisfactory and marginal preset imbalance limitsvia a dual subtractor 459. When the brake effort imbalance signal on 375is greater than the marginal preset limit from storage element 384g,then the subtractor 459 applies an appropriate output signal (e.g. highlevel) on output line F to gating circuit 462 to cause either a left orright fail indicating lamp 463 or 466 to be energized. When theimbalance signal on line 375 is less than the marginal preset limit butgreater than the satisfactory preset limit (384f) then the subtractor459 applies an appropriate output signal (output line M) to the gatingcircuit 462 which, in turn, energizes a marginal indicating lamp 464 or467. The gating circuit 462 is enabled by a readout command signal fromthe programmer 440 and is also responsive to the highest brake effortidentification signal on line 376 to transfer the output signals on thesubtractor output lines M or F to left or right indicating lamps. Wherethe left brake effort signal is the largest, the left indicating lamps(463, 464) will be energized and vice versa. When the imbalance signalon line 375 is less than the preset satisfactory level, then thesubtractor 459 applies an output signal on output line S to twosatisfactory indicating lamps 465 and 468 via the gating circuit 462.

The indicating lamps 450 through 453 and 463 through 468 inform theoperator that (1) the vehicle has passed or failed the maximum rollingresistance test, (2) the vehicle has a satisfactory, marginal orunacceptable rolling resistance imbalance, and (3) the identity of thewheel with the highest rolling resistance where the imbalance ismarginal or failing. The output signals from the gates 446 through 447and 462 may be utilized to operate a printer or other suitable recordingdevice, if desired.

BRAKE ENGAGEMENT LAG TEST

The brake engagement lag test follows the rolling resistance test. Inpreparation for this test, the computer calculates the pre-hydraulicbrake effort level for use in controlling the brake pedal actuator. Thecomponents for performing this calculation are illustrated in FIG. 8.The value of the high level brake effort for the front or rear wheeltesting sequence is obtained by a divider 469 which divides the totalbrake effort value stored in element 384a by a number representing thepercentage of such value to be used in testing the front or rear wheelbrakes, i.e. 75%, 25%, etc. The highest rolling resistance value Z asstored in element 457 in the previous test is subtracted via subtractor470 from the output signal Y of the divider 469.

The pre-hydraulic brake effort factor X₁ which has been preset intoelement 384c is divided into the difference signal Y - Z from thesubtractor 470 by a divider 471. The quotient ##EQU1## is then added tothe stored highest rolling resistance signal Z by an adder 472 and theresultant signal is stored in storage element 473.

The system is now ready for the brake engagement lag test. Referring nowto FIG. 9, force is applied to the brake pedal at a slow rate (e.g. 25pounds of brake effort per second) via the slow rate control unit 435,the brake actuator transducer 351 (electric to fluid pressure signaltransducer) and the brake pedal actuator control unit 332. The right andleft brake effort signals on lines 372a and 372b are monitored by a pairof increase in level detectors 475 and 476 to sense an increase in brakeeffort level which indicates that the respective brake has engaged. Theincrease in level detectors 475 and 476 are identical except that thestored right rolling resistance signal is used in detector 475 and theleft stored rolling resistance signal is used in detector 476. Only theindividual components of the detector 475 are depicted in FIG. 9.

The increase in level detector 475 includes an adder 478 which receiveson one input the stored rolling resistance signal for the right wheelfrom storage element 455. The other input of the adder 478 receives asignal from a preset increment storage element 480. The signal from thestorage element 480 represents a preset increment in the brake effortlevel, for example, three lbs. The output of the adder 478 is applied toone input of a subtractor 481, the other input of which is connected toline 372a to receive the right brake effort signal.

The subtractor 481 produces an appropriate output signal (high level) online 482 when the instantaneous value of the right brake effort signalis greater than the stored rolling resistance of the right wheel plusthe preset increment from storage element 480. This high level signalmay be provided by the carry line in the subtractor as is discussed inmore detail in reference to FIG. 8. By the same token, the increase inlevel detector 476 produces an appropriate output signal (high level) online 483 when the value of the left brake effort signal has increased apredetermined nominal amount (e.g. 3 lbs.) over the stored rollingresistance signal for the left wheel. Thus a high level output signal oneither line 482 or 483 is representative of the fact that the respectivebrake has engaged. The output signals on lines 482 and 483 are appliedto two inputs of a logic circuit 484.

Logic circuit 484 when enabled by an enabling signal from programmer 440produces a brake engagement lag signal (i.e. high level) on line 485upon the occurrence of an output signal (high level) from each increasein level detector 475 and 476 indicating that both brakes have justengaged. Thus the brake engagement lag signal from the logic circuitry484 marks the time when the last to engage brake has engaged. The outputsignal from the logic circuitry 484 enables gating circuits 486 and 492.

A signal representing the stored rolling resistance imbalance fromstorage element 458 is subtracted from the brake effort imbalance signalon line 375 by means of a subtractor 487. The difference or outputsignal from the subtractor 487 represents the net brake effortimbalance, that is, the gross brake effort imbalance between the rightand left wheels minus the stored rolling resistance imbalance. Theoutput signal from the subtractor 487 is applied to a dual subtractor488 and a single subtractor 490 which compare the net braking effortimbalance with preset satisfactory, marginal and invalid limits fromstorage elements 384h, 384i and 384j, respectively. If the net brakeeffort imbalance (at the instant that the last to engage brake engages)exceeds a value represented by the invalid preset limit, an outputsignal (i.e. high level) is applied to the gating circuit 492 viainvalid line to energize invalid indicating lamp 493. Energization ofthe invalid lamp 493 informs the operator that the hydraulic restrictiontest to follow cannot be validly run until certain mechanical problemscausing the unacceptable brake imbalance are corrected.

The dual subtractor 488 of FIG. 9 functions in the same manner as thedual subtractor 459 of FIG. 7 and energizes left or right marginal orfail indicating lamps depending upon the logic of the highest brakeeffort identification signal on line 375. A net brake effort imbalancesignal which is greater than the marginal limit will produce anappropriate output signal (high level) on the F output line from thedual subtractor 488 and cause the gating circuit 486 to energize a leftfail indicating lamp 495 if the left brake is the weaker brake. If thenet brake effort imbalance signal is less than the marginal limit butgreater than the satisfactory limit, the subtractor 488 will provide anoutput signal on line M to cause the gating circuit 486 to energize aleft or right marginal indicating lamp 496 or 499 depending upon whichbrake is the weakest. A net brake effort imbalance signal having a valueless than the satisfactory preset maximum limit will cause energizationof a satisfactory indicating lamp 497 and 500. The lamp indicators 493,495 through 500 inform the operator of (a) whether the brake effortimbalance at the moment that the last to engage brake has engagedexceeds the satisfactory maximum limit, falls between the satisfactorylimit and the maximum marginal limit or exceeds an invalid maximum limitand (b) which brake is lagging in performance.

The brake analyzer apparatus and method of my invention described abovemeasures and compares certain braking performance characteristics suchas brake effort imbalance when the strongest brake reaches apredetermined brake effort, e.g., pre-hydraulic, comfort level and highlevel. It should be understood that the brake effort level used for suchtests may be the sum of the individual brake efforts of the two wheelbrakes under test instead of the brake effort reached by the strongestbrake. It is only necessary that at least one of the brake effortsignals (e.g., one or the sum of both signals) reach a signalrepresentative of a pre-established brake effort to analyze certain ofthe vehicle braking performance characteristics discussed above.

Logic circuits which may be used in the block diagrams discussed inFIGS. 7 and 9 are illustrated in copending application Ser. No. 382,538.

There has thus been described an automatic brake analyzer for evaluatingthe brake engagement lag phenomena of a vehicle's brakes. Variousmodifications to the circuits will be obvious to those skilled in theart without departing from the scope of my invention as defined by theappended claims.

What is claimed is:
 1. In an apparatus for analyzing the brakingperformance of a wheeled vehicle having wheel brakes individuallyassociated with at least two wheels and a brake actuator forsimultaneously applying the brakes of said wheels, the combination whichcomprises:test means for rotating said wheels of the vehicle; brakeeffort signal generating means including the test means for producing aseparate brake effort signal for each wheel, the brake effort signalsbeing proportional to the brake effort of the respective wheel while thewheel brakes are being applied; and means responsive to the brake effortsignals for producing a brake engagement lag imbalance signalrepresentative of the difference between said brake effort signals whenthe last to engage brake has engaged after operation of the brakeactuator.
 2. The combination as defined in claim 1 including meansresponsive to the brake effort signals for producing a signalidentifying the brake which engages last.
 3. The combination as definedin claim 1 including means responsive to a brake engagement lagimbalance signal for producing a satisfactory or fail brake engagementlag imbalance signal when the brake engagement lag imbalance signal isless than or exceeds a preset maximum acceptable imbalance value.
 4. Thecombination as defined in claim 3 including means responsive to thebrake engagement lag imbalance signal for producing a marginal brakeengagement lag imbalance signal when the brake engagement lag imbalancesignal falls within a preset range of marginal imbalance values.
 5. Thecombination as defined in claim 3 including indicating means responsiveto the satisfactory or fail brake engagement lag imbalance signal forproviding a recorded indication thereof.
 6. The combination as definedin claim 1 wherein the brake effort signal generating means produces aseparate gross brake effort signal for each wheel, the gross brakeeffort signal being proportional to the sum of the braking effort androlling resistance of each respective wheel, and further including:meansresponsive to the gross brake effort signals for producing a gross brakeeffort imbalance signal proportional to the difference between the grossbraking efforts of said two wheels; rolling resistance imbalance signalgenerating means for producing and storing a rolling resistanceimbalance signal representative of the difference between the rollingresistance of said two wheels when the brakes are released; and meansresponsive to the gross brake effort imbalance signal and the rollingresistance imbalance signal for producing a net brake effort imbalancesignal proportional to the difference between the gross braking effortimbalance and the rolling resistance imbalance of said two wheels. 7.The combination as defined in claim 1 wherein the means for generatingthe brake engagement lag imbalance signal includes means for producing abrake engagement lag signal when the last to engage brake has engagedupon application of the wheel brakes, and means responsive to the brakeengagement lag signal and to the brake effort imbalance signal forproducing the brake engagement lag imbalance signal representative ofthe value of the brake effort imbalance upon occurrence of the brakeengagement lag signal.
 8. The combination as defined in claim 7including:means responsive to the brake engagement lag imbalance signalfor producing fail brake engagement lag imbalance signal when the brakeengagement lag imbalance signal exceeds a preset maximum acceptable lagimbalance value.
 9. The combination as defined in claim 7 includingmeans responsive to the brake engagement lag imbalance signal forproducing a marginal brake engagement lag imbalance signal when thebrake engagement lag imbalance signal falls within a preset range of lagimbalance values.
 10. The combination as defined in claim 7 includingmeans responsive to the brake engagement lag imbalance signal forproducing a satisfactory brake engagement lag imbalance signal when thebrake engagement lag imbalance signal falls within a pre-determinedacceptable range.
 11. In an apparatus for analyzing the brakingperformance of a wheeled vehicle having wheel brakes individuallyassociated with at least two wheels and a brake actuator forsimultaneously applying the brakes of said wheels, the combination whichcomprises:test means for rotating said wheels of the vehicle; brakeeffort signal generating means including the test means for producing aseparate brake effort signal for each wheel, the brake effort signalsbeing proportional to the brake effort of the respective wheel while thewheel brakes are being applied; brake effort imbalance signal generatingmeans responsive to the brake effort signals for producing a brakeeffort imbalance signal representative of the value of the brake effortimbalance; means responsive to the brake effort signals for producing abrake engagement lag signal when the brake effort signal of the last toengage brake has increased a preset amount over the signal representingthe rolling resistance; and means responsive to the brake engagement lagsignal and to the brake effort imbalance signal for producing a brakeengagement lag imbalance signal representative of the difference betweensaid brake effort signals when the last to engage brake has engagedafter operation of the brake actuator.
 12. The combination as defined inclaim 11 including means responsive to the brake effort signals forproducing a signal identifying the brake which engages last.
 13. Thecombination as defined in claim 11 including means responsive to a brakeengagement lag imbalance signal for producing a satisfactory or failbrake engagement lag imbalance signal when the brake engagement lagimbalance signal is less than or exceeds a preset maximum acceptableimbalance value.
 14. The combination as defined in claim 13 includingmeans responsive to the brake engagement lag imbalance signal forproducing a marginal brake engagement lag imbalance signal when thebrake engagement lag imbalance signal falls within a preset range ofmarginal imbalance values.
 15. The combination as defined in claim 11wherein the brake effort signal generating means produces a separategross brake effort signal for each wheel, the gross brake effort signalbeing proportional to the sum of the braking effort and rollingresistance of each respective wheel, and further including:meansresponsive to the gross brake effort signals for producing a gross brakeeffort imbalance signal proportional to the difference between the grossbraking efforts of said two wheels; rolling resistance imbalance signalgenerating means for producing and storing a rolling resistanceimbalance signal representative of the difference between the rollingresistance of said two wheels when the brakes are released; and meansresponsive to the gross brake effort imbalance signal and the rollingresistance imbalance signal for producing a net brake effort imbalancesignal proportional to the difference between the gross braking effortimbalance and the rolling resistance imbalance of said two wheels.